1. Technical Field of the Invention
The present invention relates to a blowby gas ventilation system for a four-stroke-cycle internal combustion engine.
2. Background Art
It is known that, in a small-sized internal combustion engine in a small-sized vehicle such as a motorcycle, a blowby gas that leaks into a crankcase is recirculated to an air cleaner (see, for example, Patent Document 1).                [Patent Document 1]        Japanese Utility Model Publication No. Sho 56-46015        
The blowby gas treatment apparatus disclosed in Patent Document 1 includes a blowby gas extraction pipe. A proximal end of the blowby gas extraction pipe is connected to an extraction port drilled in a crankcase. The blowby gas extraction pipe extends outwardly so that a distal end thereof is connected to an air cleaner through a separator.
The blowby gas extracted from the crankcase is separated into a gaseous content including a combustible content and a liquid content including an oil and the like. The gaseous content is recirculated to the air cleaner, while the liquid content is stored in a storage pipe before being exhausted.
Another arrangement is known, in which a good part of an oil content is separated in a breather chamber from the blowby gas leaking into the crankcase; the resultant blowby gas is introduced through a blowby gas guide pipe into a secondary air supply pipe before being burned in an exhaust manifold (see Patent Document 2).                [Patent Document 2]        Japanese Utility Model Publication No. Sho 62-42098        
In the arrangement disclosed in Patent Document 1, the blowby gas is not forcibly extracted. The blowby gas therefore stagnates to some extent in the crankcase. During this period, a water content and a gasoline content that enter the crankcase with the blowby gas become saturated therein. As a result, the water content and the gasoline content are mixed with, and thus dilute, the oil. The oil is then deteriorated.
The arrangement disclosed in Patent Document 2, on the other hand, is not interested in an idea of introducing fresh air into the crankcase. The arrangement is therefore unable to discharge the blowby gas efficiently.
Although the known devices have some utility for their intended purposes, a need still exists in the art for improved handling of blowby gases from internal combustion engines. In particular, there is a need for an improved blowby gas ventilation system for use on internal combustion engines, and for methods of using the improved system.